1. Field of the Invention
The present invention relates to a guide allowing mechanical linear motion, more particularly, to a linear ball bearing unit for guiding linear motion which unit develops less friction resistance against linear motion owing to the use of bearing.
In one aspect, this invention relates to a linear ball bearing unit made of a linear ball bearing and an elongated track shaft. The linear ball bearing consists of balls, a half-split bearing case, which in turn is formed by splitting an elongated square bar presenting a plurality of guide grooves for the balls along diametrically opposing two grooves, and a half-split ball retainer also presenting a plurality of guide grooves of the balls. The elongated track shaft is assembled with said linear ball bearing. The line passing through a first point of contact between a loaded ball and its corresponding R-groove in the track shaft and a second point of contact between the same loaded ball and its corresponding R-groove in the bearing case meets a horizontal line at an acute angle. The line passing through a third point of contact between another R-groove in the track shaft and one of the balls in the same groove and a fourth point of contact between the same one of the balls and its corresponding R-groove in the bearing case meets a vertical line at an acute angle. In another aspect, this invention relates to a method for manufacturing the above linear ball bearing unit.
2. Description of the Prior Art
The present inventor developed previously a bearing case for linear ball bearing capable of bearing heavy load. After forming guide grooves for balls in an elongated square bar, it was necessary to cut away both lower portions of the inner cylindrical wall in an upward and inward direction with respect to the central axis thereof to form a pair of axially extending recesses adapted for assembling a track shaft with the thus-formed bar. It was also required to thicken certain portions of the bar in order to reinforce the strength of such portions. However, such a thick wall may not be required where a bearing case is not subject to heavy load. Thus, the production method of the abovedescribed prior art is accompanied with drawback that the material would be wasted when a bearing case of a light-load rating is manufactured.
The inventor of the present invention has conducted an extensive research to solve the above drawback of the prior art method. As a result of the research, the present invention has been completed.